Apparatus for the manufacture of helical heat exchange fins



R. w. SHOEMAKER APPARATUS FOR THE MANUFACTURE OF HELICAL HEAT EXCHANGEFINS 4 sheets-shale; 1

Filed Aug. 1, 1940 INVENTOR RIMSHOEMAKER ATTORNEY R. w.- SHOEMAKER2,370,265

. Feb. 27, 1945.

Feb. 27, 1945. R w SHOE-MAKER I 2,370,265 v APPARATUS FOR THEMANUFACTURE OF HELICAL HEAT EXCHANGE FINS Filed Aug. 1, 1940 4Sheets-Sheet 3 INVENTOR R. Hf SHOE MAK ER ATTORNEY Feb. 27, 1945. R. w.SHOEMAKER 2,370,265

APPARATUS FOR THE MANUFACTURE OF HELICAL HEAT EXCHANGE FINS Filed Aug.'1, 1940 4 Sheets-Sheei 4 5 INVENTOR 5 RMSHOEMAKER "52 Y A'i'TbRNEYPatented F eb. 27, 1945 APPARATUS FOR THE MANUFACTURE OF HELICAL HEATEXCHANGE FINS Richard W. Shoemaker, Woodbury, Conn.

Application August 1, 1940, Serial No. 349,099

9 Claims. ('Cl. 164-37) My invention relates to a novel method andapparatus for the fabrication of helical heat exchange fins, and moreparticularly to a method and apparatus for fin fabrication whichconstitutes a distinct improvement over the disclosure of United StateLetters Patent 2,154,430, granted April 18. 1939. and its continuationsin part United States Letters Patent 2,155,395, granted April 25, 1939.and 2,162,693, granted June 20, 1939.

The method described in these above numbered patents for fabricatinghelical heat exchange fins essentially comprises the steps ofprogressively cutting a bar of metal continuously at its end and in thedirection of its length to directly form by the cutting operation thedesired helical heat exchange fin. While the patented method is entirelyoperative. it possesses the inherent disadvantage that it will not necessarily and continuously result in the production of helical heatexchange fins having commercial uniformity of predetermined dimensionsto permit their ready attachment to a heat exchange element,particularly when the cutting of the fin is carried on continuously overprotracted periods.

The outside and inside diameters of the severed helical fin arecontrolled by the dimensions of the cylindrical bar stock,,speed ofcutting, and location of the cutting edge, all of which are controllableand uniform. Its dimensions are also determined by the relativesharpness of the cutting tool a ong the line of cleavage, by the weightof the severed fin resting against the cutter and exerting a force onthe metal of the fin at the line of cleavage. and by the uniformity ofthe bar stock from which the fin is severed. It is obvious that thesharpness of thetool will vary with its hours in service, that the barstock will not be perfectly uniform, and that the weight ofthe severedfin will varv as it progressively accumulates on the takeoff rod. Thisgradual augmentation in frictional forces exerted on the line'ofseverance, progressive diminution in'the sharpness of the cutting tool,and unavoidable cc'asional hard spots in the cylindrical bar stock, a lare apt to have a detrimental effect upon the helical heat exchange finbecause, since they are variable, they tend to render the dimensions ofthe severed fin variable. It is essential to economically produce ahelical fin of predetermined and uniform dimensions in order toconveniently assemble the fin with its associated heat ex-' changeelement. These deficiencies in the-prior a'rtare effectively overcome bythe present invention in which the improved method of and apparatus forfin fabrication contemplates the steps of progressively cutting a bar ofmetal continuously at its end and in the direction of its length todirectly form by the cutting operation a helical heat exchange tionallathe and a suitable cutting tool in conjunction with a novel guide, Iprefer to practice the same with a lathe of extra substantialconstruction to eliminate vibration, with a head stock provided with anoversize hole to accommodate large sizes of fin stock, with a positivecarriage feed instead of the customary friction devices, with a gear boxto provide accurate adjustment in feed between .003 inch and .010 inch,and with a substantial follower rest of the sleeve and roller bearingtype to rigidly support the rotating fin stock as close as possible tothe cutting edge. Furthermore, I prefer a wedge-shaped cut-' ting toolnot supported like a cantilever in the customary tool holder, butsupported firmly from all four sides and at the bottom to transmit thecutting thrust directly to the carriage of the lathe, and alsomechanically connected to the follower rest to preserve the relativepositions of of the helical heat exchange fin, whereby to con-' fine thesame adjacent to'its line. of severance to a predetermined and generallyunnatural path of movement principally by engagement of a portion of theperipheral wall of the guide with the peripheral edge of the severedfin.

The successive convolutions of the helical heat exchange fin emergingfrom the recessed guide are supported in any suitable manner with theimportant result, however, that the progressively increasing frictionalforces heretofore exerted by the gradually accumulating cut 'fln'against the cutting tool now act against the exterior surface of therecessed guide. This has the highly beneficial effect of keeping thefrictional forces exerted between the cutting tool and that portion ofthe severed fin in immediate contact therewith substantially constantduring the long continued cutting operation. Thus by confining the finadjacent it line of cleavage to a predetermined unnatural path ofmovement and maintaining the frictional forces acting upon said fin inits unnatural confined path of movement substantially constant, there isproduced a helical heat exchange fin of substantially uniformdimensions, even thoughthe cutting operation proconvolutions of theseveral helical heat exchange Other objects and many of the attendantadvantages of this invention will be readily appreelated as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanying sheetsof drawings, wherein there are depicted by way of example certaininstrumentalities for carrying the method into effect, and in which:

Fig. 1 is a view in perspective of one embodiment of the guide;

- Fig. 2 is likewise a view in perspective of a cutting tool that may beemployed;

Fig. 3 is a view in section showing the recessed guide and cutting toolin juxtaposed relation;

Fig. 4 shows the assembled guide and cutting tool of P18. 3 viewed froma diner-ent angle;

Fig. 5 further delineates perspectively the guide of Fig. 1 as seen froma difierent viewpoint;

Fig. 6 depicts in end elevation the assembled cutting tool and guidemounted on the tool holder and positioned in cutting relation withrespect to the bar from which the helical heat exchange fin is beingsevered;

Fig. 6A is a sectioned view of Fig. 6 in side elevation depicting thebar in cutting relation to the assembled cutting tool and guide togetherwith a rod for supporting the convolutions of the helical fins as theyemerge from the recessed guide;

Fig. '7 is an end elevation showing another embodiment of the guide inwhich the guide and cutting tool are integral and the rear wall surfaceis omitted over the arcuate recess of the uid Fig. 9A is a plan viewshowing the method of supporting the sides of the cutting tool andguide;

Fig. 9B is a side view showing the method of supporting the cutting tooland guide on the bottorn from the bed of the lathe;

Fig. 9C is a diagrammatic sketch in plan to show the angular limits inthe horizontal plane which the takeoff rod may assume with respect tothe axis of the bar from which the helical heat exchange fin is beingcut;

Fig. 9D is a side view showing these limits in the vertical plane;

Fig. 10 is an enlarged view in perspective of the cutting tool and guideas shown in Fig. 8, to illustrate the action of the cutting tool at theline of severance and the reaction of the guide at the line ofseverance;

Fig. 10A is a section through plane AA on Fig. 10 to depict the flowageof metal at the line of cleavage of the cutting tool.

Before proceeding with a detailed description of the present invention,it is deemed expedient in the interest of clarity to make certainremarks concerning the bar' from which the helical heat exchange fin isto be severed. While the bar as depicted in the drawings is shownlongitudinally apertured with both the inner and outer surfaces thereofsubstantially cylindrical in contour, it is to be distinctly understoodthat the method of the resent invention is not limited to this preciseconfiguration since other shapes or contours may be employed where thisis found .desirable, provided only that either the inner Fig. 8 depictsstill another embodiment of the or the outer surface of the bar becylindrical in shape. The bar is longitudinally apertured to the samecontour and substantially the same dimension as the outer surface of theheat exchange element which it is designed to surround.

As for the metal of the bar,- it may be either.

ferrous or non-ferrous, the latter being preferred by reason oi itsgreater ductility, high heat conductivity, and freedom from corrosion.Very satisfactory results, however, have been obtained from both ferrousand non-ferrous metals, and particularly from cooper, brass, andaluminum in the latter group. It is also highly desirable for the metalof the bar to be as uniform and free as is commercially practicable,from non-metallic inclusions and segregations of impurities for reasonswhich will be apparent as the invention becomes better understood.

Turning now to the drawings, there is shown in Fig. 2 and other figuresthereof a cutting tool identified in general by the reference characterI that many be advantageously utilized in carrying out the method of myinvention. The tool'is provided with a side rake surface 2 at a suitableangle 3 with respect to the vertical and a cutting edge 4 which isground at the desired angle 5 with respect to the horizontal. Thesurface 6 of the tool that opposes the stock being cut is ground at a.suitable angle I of inclination from the vertical to provide clearanceand prevent frictional bind ing and consequent chattering. It isto beunderstood that the cutting tool may assume any of a number of formswithin the purview of the present invention and that the specific formdelineated in the drawings is given only by way of example. None of theangles given are critical, and the cutting edge may be horizontalinstead of cambered by the angle 5, although it has been found that thepositioning of the tool can be more easily adjusted and better controlof the final dimensions of the severed helical fin is obtained by theuse of a tool which is cambered to give shearing action. a

The guide, as disclosed, more particularly in Fig. 1 and identifiedgenerally by the reference character 8, has its inner surface 9angularly disposed in a manner to insure its substantially Imetal-to-metal conformity with the side rake surface 2 and verticalsurface 2a of the cutting tool where the tool and guide-are superimposedin the manner illustrated in Figs. 3 and 4. The angular deviation of theedge IU of the terminal face I l of the guide from the horizontal andthat of the outer surface l2 of the guide from the vertical correspondrespectively to the angular deviation of the cutting edge 4 and siderake surface 2 of the cutting tool, in consequence of which these angles5 and 3, respectively, have been designated by similar referencecharacters.

The guide is provided with a recess l3, the outer peripheral wall M ofwhich is preferably arcuate or curvilinear in contour and with acurvature which may be substantially the same as theouter peripheralsurface of the severed helical fin and which forms with the cutting toola passage for the reception of the severed fin which groove or passageis substantially wider than the severed fin. The peripheral wall I4 ofthe recess by engagement with the peripheral surface of the serered finimparts to the fin a fixed outer uniform dimension, as well as a uniforminner dimension when the bar is longitudinally apertured since the widthof the severed fin 21 in Fig. 6A is invariably equal to the wallthickness of the bar stock from which the fin is being cut, and hencethis dimension has been designated by similar reference characters 21 inFig. 6A. The depth of the recess as indicated at l5 in Fig. 3'is such asto adequately accommodate the thickness of the fin being severed.

For facilitating the entrance of the severed fin into the passagewayprovided therefor. the terminal face I l of the guide is verticallymachined and spaced a proper distance Hi from the cutting edge 4 of thetool. The magnitude of this spacing will vary with the task at hand andhence is not deemed critical, and it may be adjusted by a spacer plate24 depicted in Fig. GAof the drawings. 7 Furthermore, that part of theperipheral wall M in the recess of the guide adjacent to the cuttingedge of the tool should extend beyond the outer surface of the bar l1under severance in order to provide for unimpeded lateral access of thesevered fin into the passage. Similarly, the recess provides ampleclearance for the inner peripheral edge of the longitudinal aperture inthe bar stock H. The amount of this clearance, indicated by thedimensional lines at IS in Fig. 6 0f the drawings, is likewise notcritical and may be adjusted by the cross feed 29 (Fig. 9B) of thelathe. I

The assembled tool and guide are mounted on the tool holder, identifiedin general by the reference character I9; as shown in Fig. 6 of thedrawings. A plan view 01; this mounting is depicted in v Fig. 9A. Thistool holder includes a member 20 recessed to receive the cutting tooland a clamping plate 2| for holding the assembled tool and guide infixed relation to the member 20 and the stock being cut. This clampingplate may be removably secured to the member 20 by any suitable means.such as bolts. 22. The tool holder I9 is mounted on the conventionalcross feed 29 in Figs. 9 and 93 to provide transverse movement and thiscross feed 29 is in turn mounted on the carriage 30 of the lath as shownin Figs. 9 and the tool holder l9 instead of being supported by thecustomary tool post where the tool acts as a cantilever. The tool isalso supported on four sides by the tool holder I9 and the clampingplate 2|, as shown in Fig. 9A, with the result that all chatter isobviated and the tool ismaintained in juxtaposed relation to the barstock being cut.

As the convolutions of the severed fin emerge from the recess of theguide, as shown more particularly in Fig. 6A of the drawings, .theyproceedtupwardly and over the outer surface l2 of the guide and at thesame time assume a revolving position on the takeoff rod 23 which issupported at one end by means of a pin 26 iii-- sorted in an aperture 25of the guide.

'In Fig. 9 the bar stock I! is shown mevolubly mounted in a lathe havinga headstock 38with an unusually large hole to take large sizes of finsand with a steady rest 33 carrying the end of the bar stock I! in abushing supported in a roller bearing with the minimum possibleclearance. The steady rest bearing is bolted rigidly to the lathecarriage 30 holding the stock I! in the axis of rotation. The takeoffextension 34 is rigidly attached to the lathe carriage 30 and thetakeoff rod upright 35 is in turn rigidly attached to the extension. Theslide 36 on the takeofi upright. 35 carries one end of the takeoff rod23 at the articu-- lated joint 31 and the other end of 'the takeoff rodis supported by the'hole 25 in the guide.

Fig. shows the limits of angularity of the takeoff rod with the axis ofrotation of the stock in the horizontal plane and Fig. 9D in thevertical plane. These angles are not critical and may be varied withinwide limits by the slides and ar- .OlOinch. The feed control is positiveacting instead of being provided with the usual friction-devices.

I "Having fully described the apparatus embody-- ing the means forpracticing the method of my invention, the principle involved inpredetermining the dimensions of the severed helical heat exchange flnswill now be set forth. In setting up-the apparatus above described.

"the bar stock I1. is first rigidly secured in the-- special headstock38' and steady rest 33} Next, to obtain the approximate juxtaposedrelation between the tool I and the stock H, a washer 31 is shown inFig.- 6A which may be of. anyi'desired thickness. To obtain fineadjustmentslfthe operatorcan adjust the position of the cut ng edge 4 bymeans of the customary cross feed 29 to which is secured the toolholder'l9 bolts 32- shown in Figs. 9, 9A and 9B. The angle of inclination Set the cutting edge 4 from? the horizontal in additiontoshearing permitSN-lthe line of severance to be -adjusted to the desiredposition 1 with respect to the axis of rotation of the bar I! by meansof the cross feed plate 29. The location of the cutting edge 4 withrespect to the axis of rotation of the bar stock I! is thereforeadjustable by both the washer 3| and the cross feed 29. The guide 8 hasnot yet been assembled in the tool holder. The cutting tool ispositioned in relation to the work being cut in accordance withexperience with the material to be cut, the feed to be used, the cuttingspeed, and the finish desired.

The feed of the lathe carriage is then set to give the thickness of cutdesired remembering that the thickness of the final helical heatexchange fin designated by the reference character 40 in Figs. and 10Awill be as much as approximately twice the carriage feed 4|. This isexplained by the fact that the metal of the bar stock I! piles up fromplastic flow at the line of severance 4 as depicted in the section viewNext the lathe is started and the bar I! is rotated in the customarymanner and an initial cut of a few turns of the helical heat exchangerfin is made. If this initial shaving is not'larger by a substantialamount than the outside diameter of the bar stock and the final diameterdesired. the cross feed is adjusted to increase or decrease the verticaldistance 39 the cutting edge 4 bein sloped) between the extended line ofseverance 4' and the center of rotation C of the bar stock asindicatedin Fig. 10. By varying this distance the dimensions of thehelical fin-may be altered between narrow limits to obtain a normaloutside diameter of fin when cutting freely which is substantiallylarger than the diameter of the bar stock IT.' The final predetermineddiameter of the helical heat transfer fin should be approximately thatof the bar stock I! because a large difference between the two diametersincreases the embrittlement and gives the heat transfer fin undesirablephysical properties.

Having obtained an initial cut or shaving ofthe desired increaseddimensions over those of the bar stock 11. the guide 8 is positionedwith respect to the tool I and bar stock l1 so that there will be ampleclearance l8 and so that the point 45 in Fig. 10 of the drawings on theperipheral recess wall l4 of the guide 8 will be spaced from the axis ofrotation of the severed fin the distance 46 (Fig. 6A) to give the finalheat exchange fin the radius 45 desired. This distance 46 is the finalfin radius; and the predetermination and control of this measurement isa salient feature of my present invention.-

It must be clearly understood that the distance of the point 45 from thecenter of rotation of the bar stock. I! will not be equal to thedistance 41 unless the final outside diameter of the fin is desiredexactly equal to the bar stock, and the line of severance of the cuttingtool I intersects the axis of rotation of the bar stock l1. Since,however, this line of severance and the center from which is struck thearcuate recess wall I 4 are displaced from the axis of rotation of thebar stock' IT, by the distance 39, the distance of point 45 from theaxis of the bar I! is not normally equal to the radius of the severedhelical heat transfer fin nor to the radius of bar stock l1. However, itis always true that the point of engagement of the fin with the recesswall at 45 is at a distance from the axis of rotation of the severedheat exchange fin whichappears to be exactly equal to the desired radius46 of the heat exchange fin.

Upon initiation of the cutting operation, the fin severed from the barmoves downwardly from the cutting edge of the tool and enters the recessor slot l3 of the guide positioned. in juxtaposed relation to thecutting tool. At the upper portion of the recess the severed fin doesnot engage the peripheral recess wall l4 owing to the clearance l8, butas the fin moves downwardly the peripheral surface gradually approachesthe recess wall and engages the same in the manner shown in Figs. 6 and6A of the drawings. This peripheral engagement of the severed fin withthe recess wall of the guide occurs just prior to the fins emergencefrom the recess and imparts to the fin a predetermined inner and outerdimension; and, at'the same time, has a tendency to keep the peripheraledge of the fin smooth, thus eliminating as far as possible theformation of a serrated edge.

Study of Fig. 10 will disclose the method by which the pressure exertedat 45 controls the outside and entirely dependent inside diameters ofthe severed fin. As the metal of the bar stock l1 approaches the line ofseverance 4 plastic flow occurs in the area marked'49 (Fig. 10A) and themetal is piled up on the cutter I to such an extent that the thickness40 of the severed material is approximately twice that of the feed 4|and the fin material wrinkles up in a corrugated fashion, as shown bymicroscopic studies. It should be noted in this connection that Figs. 10and 10A are exaggerated and enlarged representations of the plastic flowand corrugation of the metal at the line of severance. Since the finwould have an outside diameter substantially larger were it not for therestraining force exerted by the guide, at point 45, that force exerts apressure in the area of plastic flow marked 42 which increases thenormal size of the corrugations or wrinkles and maintains the outsidediameter constant as long as any engagement or pressure whatsoeverexists at 45. It is to be noted that the force exerted on the fin by theguide in the area 45 acts through a substantial lever arm. The leverconsists of the severely cold worked and hardened metal of the severedfin in the area 50. Also, the metal of the fin appears to be permanentlyset immediately as it undergoes transition at the line of severance 4,and so much so that no change in the curvature which determines theoutside and inside diameter can occur outside the area of plastic flowwithout undesirable effects. This area may be reduced in temperature bymeans of a coolant such as cutting oil. After the fin leaves the recessin the guide at point 45, therefore, no changes occur in its dimensions.

The'necessity for the restrictive force at 45 in maintaining accurateand predetermined dimensions of the severed helical fin is apparent ifthe effect of the variable factors on the plastic flowat the line ofseverance 4 is studied. ,These variable factors, which cannot becontrolled, are caused by hard spots or non-metallic segregations in thebar stock l1, unequal wear on the cutting edge 4, and constantlyaugmented friction between the severed fin and the side rake surface 2of the tool. In Fig. 10 at point 53. the peripheral edge of the fin isshown as it would clear the cutting tool l were it permitted to assumeits natural shape as it does during the preliminary cut.

If a hard spot in the stock occurs at the area 42, near the innerperiphery, plastic flow will increase, the folds in the severed fin willthicken, and the linear and angular velocity of the sevcred finmaterially decrease in the area 42. In the area 43 and along theremainder of the cutting edge 4, the thickness and velocity will remainunchanged and the fin will swing to the right to point and cause adecrease indiameter from that desired. The peripheral edge of this fin,if it were free, is shown clearing the cutting tool at point 5| insteadof at point 53. A relatively dull spot in the cutting edge 4 .appears tohave exactly the same effect if the dullness occurs in the area 42 or itis apparent that duller cutting edges will increase the size of thefolds.

Conversely, if the hard spot in the bar stock I! occurs in the outerperiphery in the area 43, the fin will open and have an increaseddiameter if it is not prevented from so doing by the pressure at point45 of the guide 8. The peripheral edge of this fin is shown leaving theedge of the cutting tool at point 52 instead of the point 53.

With theguide in place, however, the effect of increased plastic flow t42 is to decrease the pressure, and at 43 to increase the pressureexerted 'by the fin on the recess in the guideB at 45, and so long asthe decrease in pressure at point 45 caused by increased plastic flow at42 does not exceed the normal force exerted at point 45 to cause thesevered fin to clear the guide completely at point 45, the dimensions ofthe fin will continue to remain uniform even though the cuttingoperation proceeds without intermission over protracted periods.-Excessively increased pressure at 45 caused by similar phenomena atpoint 43 will merely cause abnormal hardness or breakage of the severedfin.

For instance, experience has demonstrated that when using selectedcopper in the bar stock the normal force exerted at 45 in reducing theoutside diameter a sixteenth of an inch is never completelycounter-balanced by the variable I one-sixteenth of an inch is givenonly by way of illustration, that it is not critical, that it will varywith the'material to be cut, the cutting speed, and the shape of thetool and dimensions of the. severed fin.

As the cutting operation proceeds, the severed fin,- which is emergingfrom the recess of the guide, progressively accumulates on the rod 23and the mass of this accumulated fin exerts a force on the rod andagainst the outer surface l2 of the guide which is substantiallyparallel to the side rake surface 2 of the cutting tool. By virtue ofthis arrangement the force exerted against that portion of the severedfin in immediate contact with the side rake surface 2 of the cuttingtool 'is'maintained substantially constant resulting in substantiallyconstant frictional forces acting between cutter and the severed fin incontact therewith. This variablefrictional force would result inincreasing the outer diameter of the severed fin as it accumulateson therod and increase the pressure exerted by the helical fin on theperipheral wall of the. guide at point 45 which has been found to giveundesirable physical properties or even fracture of the severed fin.

It has been found that fins may be cut of sufiiciently accurate anduniform dimensions for some commercial purposes without maintainingconstant friction between the severed fin and the side rake surface 2 ofthe cutting tool; but the di-.-

, mensions and physical properties can be predetermined with greateraccuracy by the use of a'guide with a rear wall surface I2 to supportthe severed fin. Since, however, for some purposes it is unnecessaryalternate shapes of guides without th s rear wall supporting surface areshown in Figs. '7 and 8. The guide depicted in Fig. 8 has been It hasbeen found that in practice no change in dimensions of the cut fin willoccur during the cutting of any number of bars [1 providing all are thesame material and heat treatment. If the dulling of the cutting edgeproceeds too far it is necessary to.substitute a new cutting 'tool I andif the new cutting tool is replaced with the guide in the samerelationship to the bar stock H as its predecessor, the resulting finwill be of the same dimensions as before.

According to the patent statutes I have set forth the principle and modeof operation of my invention, and have illustrated and described what Inow consider to represent its best embodiment. However, I desire to haveit understood that within the scope of the appended claims th inventionmay be practiced otherwise than as specifically illustrated anddescribed.

Having now so fully described my invention that others may therefrommake and use the same, what I claim is:

1. An apparatus for the fabrication of a helical heat exchange fin ofpredetermined dimensions comprising means for supporting a bar of metal,

a cutting tool operable to be positioned with its thecutting operation ahelical heat exchange fin and a recessed guide positioned on the cuttingtool and forming therewith a passage for the reception of the helicalheat exchange fin whereby to impose a force on the peripheral edge ofthe fin which confines the same adjacent its line of severance to apredetermined path of movement.

2. An apparatus for the fabricationof a helical heat exchange fin ofpredetermined dimensions comprising means for supporting a bar of metal,a cutting tool operable to be positioned with its cutting edge incontact with the end of the aforesaid, bar,'mea-ns for causing a.progressive and continuous cutting of the bar at its end nd in thedirection of its length to directly form by the I cutting operation ahelical heat exchange fin and a recessed guide positioned on thecutting. tool and forming therewith a passage for the reception of thehelical heat exchange fin whereby -to impose a force on the peripheraledge of the heat exchange fin of predetermined dimensions comprisingmeans for supporting a bar of metal, a cutting tool provided with acutting edge posi-' tionable in contact with the end of the aforesaidbar and a side rake surface extending downwardly therefrom. means forcausing a progressive and continuous cutting of the bar at its end andin the direction of its length to directly form by the cutting operationa helical heat exchange fin, and a recessed guide positioned on thecutting tool and extending along the side rake surface thereof to-formtherewith a passage for the reception of the helical heat exchange finwhereby to apply a force to the peripheral edge of the fin whichconfines the same adjacent its line of severance to a predetermined pathof movement, the face of the guide opposed to the end of the metal barunder severance being spaced from the cutting edge of the tool and thatpart of the recess in the guide adjacent to the cutting edge of the toolextending beyond the outer surface of the bar under severance tofacilitate the entrance of the fin into the passage provided for thesame.

4. An apparatus for the fabrication of an apertured helical heatexchange fin of predetermined dimensions comprising means for supportingan apertured bar of metal, a cutting tool provided with a cutting edgepositionable in contact with the end of the aforesaid bar and a siderake surface extending downwardly therefrom, means for causing aprogressive and continuous cutting of the. bar at its end and in thedirection of its length to directly form by the cutting operation anapertured helical heat exchange fin, a recessed guide positioned on thecutting tooland extending along the side rake surface thereof to formtherewith a passage for the reception of the apertured helical heatexchange fin whereby to apply a force to the edge of the severed finwhich confines the same adjacent its line of severance to apredetermined path of movement, the face of the guide opposed to the endof the metal bar under severance being spaced from the cutting edge ofthe tool and that part of the recess in the, guide adjacent the cuttingedge of the tool extending beyond the outer surface of the bar underseverance to facilitate the entrance of the fin into the passageprovided for the same and the progressive engagement of the peripheralrecess wall of the guide with the peripheral surface of the severed fin,and a rod extending from the aforesaid guide for supporting thesuccessive convolutions of the helical heat exchange fin emerging fromthe guide recess.

5. A guide for controlling the dimensions of a cut helical heat exchangefin comprising a member having one side thereof shaped to conform to theside rake surface of the cutting tool in conjunction with which it is tobe employed, the

said side being recessed to form with the side rake surface of thecutting tool a passage for the reception of the helical heat exchangefin whereby to apply a force to the peripheral edge of the fin whichconfines the same adjacent its line of severance to a predetermined.path of movement.

6. A guide fOr controlling the dimensions of a cut helical heat exchangefin comprising a member having one side thereof shaped to conform to theside rake surface of the cutting tool in conjunction with which it is tobe employed, the said side being recessed and terminating short of thecutting edge of the tool to form with the side rake surface thereof apassage for the reception of the helical heat exchange fin whereby toconfine the same adjacent its line of severance to a predetermined pathof movement. 4

'7. An apparatus for the fabrication of helical heat exchange fins ofpredetermined dimensions comprising in combination means for supportinga bar of metal, a cutting tool operable to be positioned with itscutting edge in contact with the end of the bar, means for causing aprogressive and continuous cutting of the bar at its end and in thedirection of its length to directly form by the cutting operation ahelical heat exchange fin, and means for impressing a force on theperipheral edge of the severed fin to con-' fine the same adjacent itsline of severance to a predetermined path of movement.

8. An apparatus for the fabrication of helical heat exchange fins ofpredetermined dimensions comprising in combination means for supportinga bar of metal, a cutting tool operable to be positioned with itscutting edge in contact with the end of the bar, means for causing aprogressive and continuous cutting of the bar at its end and in thedirection of its length to directly form b the cutting operation ahelical heat exchange fin, and means for impressing a force on theperipheral edge of the severed fin to confine the same adjacent itsline-of severance to a predetermined path of movement, the said lastmentioned means contacting the peripheral edge of the'fin at a pointspaced from the axis of rota-- tion of the severed fin a distancesubstantially equal to the desired fin dimension.

9. An apparatus for the fabrication of a helical heat exchange fin ofpredetermined dimensions comprising in combination means for supportinga bar of metal, a vertically arranged cutting tool operable to bepositioned with its cut ting edge in contact with the end of the bar,means for causing a progressive and continuous cutting of the bar at itsend and in the direction of its length to directly form by the cuttingoperation a helical heat exchange fin, and a guide associated with thecutting tool for impressing: a force on the peripheral edge of thesevered fin to confine the same adjacent its line of severance to apredetermined path ofmovement.

RICHARD w. SHOEMAKER.

